This proposal includes a number of objectives related to establishing mechanistic bases for understanding normal and altered lung function. A major aim is to further clarify the role of surface tension in lung recoil, gas trapping, foam production, alveolar stability, and lung opening. A second aim is to relate interstitial fluid volume to lung mechanics, and to examine fluid movements through pleura and interstitium. A third aim is to examine the bases for cardiogenic oscillations of trace gases in the expirate.